The present invention relates to an ink-jet printer for ejecting ink onto a paper sheet held on a rotary drum to perform printing.
Recently, personal computers of high performance and low cost has become available, and the spread of personal computers has abruptly increased. In accordance with this trend, color printers have been also increasingly demanded. At the present stage, various types of ink-jet printer exist as color printers suitable for personal use.
Conventionally, there is a known ink-jet printer which can perform a continuous printing of 500 or more sheets, for example. This ink-jet printer has a rotary drum which rotates at a predetermined circumferential speed, and a print head for ejecting color inks onto a sheet of paper held on the peripheral surface of the rotary drum. The sheet is fed to the rotary drum from the front side of the rotary drum, printing is performed in a state where the paper sheet is wound on the rotary drum. After printing, the paper sheet is separated from the rotary drum and discharged to the rear side of the rotary drum.
The print head includes nozzle units of, for example, yellow, cyan, magenta and black which are disposed along the peripheral surface of the rotary drum. Each of the nozzle units has ink-jet nozzles which are arranged across the paper sheet in the main scanning direction parallel to the axis of the rotary drum and eject inks as the rotary drum rotates. Each nozzle unit is shifted in the main scanning direction at a predetermined rate, and returned to its initial position after a predetermined number of rotations for causing the nozzle unit to be moved by a distance equal to the nozzle pitch. Each nozzle unit scans the paper sheet simultaneously in the main scanning direction and the sub-scanning direction as described above, so as to eject ink onto the entire paper sheet.
In a case where positional deviation or warp-up of the paper sheet occur when it is placed on the rotary drum of the ink-jet printer, incorrect alignment is caused between dots of color inks and significantly deteriorates the printing quality.
An object of the present invention is to provide an ink-jet printer which can prevent positional deviation of a print medium held on the rotary drum.
According to a first aspect of the present invention, there is provided an ink-jet printer which comprises a rotary drum for rotating at a constant speed, a medium loading mechanism for loading a print medium onto the rotary drum, a medium holding section for holding the print medium loaded by the medium loading mechanism on the rotary drum, and a print head for printing an image by ejecting ink onto the print medium which is held on the rotary drum by the medium holding section and rotated together with the rotary drum, wherein the medium loading mechanism has a pair of loading rollers for feeding the print medium while pinching the printing medium, and a separating mechanism for separating one of the loading rollers from the other roller to release the print medium after a leading edge of the print medium has been held on the rotary drum.
According to a second aspect of the present invention, the medium holding section of the ink-jet printer according to the first aspect has a charging roller for electrically charging the print medium while pressing the print medium onto the rotary drum, such that the print medium is held on the rotary drum by electrostatic attraction, and a separating mechanism for separating the charging roller from the rotary drum after a predetermined rear part of the print medium has passed the charging roller.
In the ink-jet printer according to the first aspect, the separating mechanism separates one of the loading rollers from the other roller to release the print medium after the leading edge of the print medium has been held on the rotary drum. When the loading rollers are spaced from each other, the print medium is set in a free state where no pinching force is applied from the loading rollers. Therefore, the rotation load on the rotary drum can therefore be reduced. In this case, since the print medium is securely held on the rotary drum, positional deviation and warp-up thereof are avoided. Thus, the printing quality is improved.
In the ink-jet printer according to the second aspect, the charging roller electrically charges the print medium loaded by the medium loading mechanism while pressing the printing medium onto the rotary drum. Therefore, charging of the print medium can be started upon loading of the print medium from the medium loading mechanism and continued until the predetermined rear part of the print medium passes the charging roller.
Furthermore, the charging roller is separated from the rotary drum after the predetermined rear part of the print medium has passed the charging roller. Thus, the charging roller would not touch the ink ejected onto the print medium even if the rotary drum is repeatedly rotated to obtain a printed image. This contributes to preserve the print in high quality.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.